Method and apparatus for repairing post-tensioned concrete

ABSTRACT

An end cap secured to a tubular member for use in repairing post-tensioned concrete, including a first segment, a second segment, and a third segment. The first segment has a first end and a first opening, where the first segment is substantially cylindrical in shape. The second segment is substantially frustoconical in shape. The third segment has a second end and a second opening and is substantially cylindrical in shape. The second segment is disposed between and integral with the first segment and the third segment. A cavity is formed by the first, second, and third segments, where the first end is arranged to be secured to a tubular member and at least one cable is disposed longitudinally within the cavity.

FIELD OF THE INVENTION

The invention broadly relates to a method and apparatus for repairing post-tensioned concrete, and more particularly, to an end cap secured to a tubular member used during the splicing and coupling of post-tensioned concrete repairs.

BACKGROUND OF THE INVENTION

Post-tensioned concrete is widely used in building structures as it provides a light, structurally efficient, durable solution for the construction of commercial office buildings, residential apartments, high-rise condominiums, and mixed-use facilities such as hotels and casinos. Post-tensioned concrete is also utilized frequently in the elevated concrete decks and sometimes in the ground floor slabs of condominium structures, including the associated parking garages. Longer, thinner slabs result in greater design flexibility and require less reinforcing steel to achieve the same strength as other methods of construction. Additionally, post-tensioned concrete greatly reduces the floor-to-floor height when compared to structural steel options, which results in significant savings in the facade, HVAC, electrical, plumbing, and vertical transportation systems. As such, post-tension concrete was introduced into residential high-rise construction as a means to reduce the thickness of the elevated concrete decks, to widen spans between column supports, and to speed up the construction process.

Generally, post-tension reinforcement includes stranded cables, also referred to as “tendons” or a “strand,” that are contained typically in a plastic sheath and are positioned in the forms before the concrete is poured. Afterwards, once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or “tensioned”, and anchored against the outer edges of the concrete. Concrete has a very high compressive strength, typically 3,000 to over 10,000 psi, but very low tensile strength, typically 300 to 400 psi. Post-tension cables provide tensile strength to the concrete. This increase in tensile strength is achieved when the cables are stressed under significant tension loads following the pouring of the concrete.

In the past, a post-tension slab was typically constructed with cables laid out in two directions, typically at 90 degrees to one another. The cables are enclosed in a plastic sheathing to separate them from, and allow for movement within, the surrounding concrete. Each cable is anchored at one end of the slab and then placed loosely across the slab to another steel anchor located at the opposite end of the slab. Two steel reinforcing bars are placed behind the anchors to help distribute the high tensions forces from the anchors. Once the steel, cables, and anchors are installed, the concrete is poured. After the concrete has reached an acceptable strength, the cable is tensioned within the concrete slab, which is achieved by pulling the cable to a force of 33,000 pounds. Two steel wedges are placed around the cable and within the anchor to lock the cable at the applied tension load.

Many early post-tension installations did not include corrosion protection of the steel anchorage and cable ends. As a result, penetration of moisture through the concrete often results in the corrosion of the post-tension cable, anchor, and wedges. The presence of corrosion can have a substantial impact on the structural integrity of the post-tension system. Additionally, a post-tension cable can be compromised when types of restoration, renovation, or remedial work are being performed on a post-tensioned reinforced structure. Moreover, post-tension cables can also be compromised when the original construction was performed poorly or maintenance of the exterior of a building is not performed on a regular basis. In any of these situations, the ends of the cables at the edges of concrete are allowed to corrode, and without proper maintenance, the corrosion can advance to the point where cables or end anchors fail.

Repair of a damaged post-tension cable is performed by typically exposing one or both ends of the damaged cable at the edges and at one or multiple locations where the cable breeched the concrete. A new cable or portion of a cable is used to replace the damaged cable. If the entire cable is replaced, the old cable is removed from the plastic sheathing within the concrete and a new cable is installed through the sheathing. The affected sheathing and the concrete are then repaired, and allowed to cure. The cable is then tensioned and the ends patched. If only a portion of a cable is replaced, the connection of the new cable to the older cable is accomplished with a post-tension cable splice and then repaired in the same fashion as replacing the entire cable mentioned above.

Due to the extremely high force in the cables, removal of the concrete behind the anchor and bars can cause a significant failure of the slab. As a result, replacement of deteriorated anchors requires de-tensioning of the affected cable. It should be noted that only the damaged portion of the cable is de-tensioned during repairs, as the remaining cable must retain post-tension force in order to maintain the structural integrity of the slab. The de-tensioning of the cable is accomplished by opening a small area of the concrete slab inward from the area to be repaired. Within this opening, a temporary cable “lock-off” device is installed. The lock-off location is generally two to three feet from the edge so that the cable forces can flow or be redirected around the opening with a risk of a concrete failure. The outer portion of the cable is then released, and repairs can begin.

During concrete repairs, replacement anchors and cables are installed. To provide protection against corrosion, plastic sheathed anchorage systems that protect all the parts of the anchors and cables are used. The cables are usually encased in a flexible plastic protective hose, typically called a sheath or duct, to prevent the cable from bonding to the concrete during placement and curing of the concrete. The protective sheathing remains in the structure. In some cases, the void between the cable and the sheath is filled with grout. In this manner, the cable becomes bonded to the concrete section and corrosion of the steel cable is prevented. In other cases, the cable is coated with grease prior to placement into a protective sheathing. Cables of this type are not pressure grouted after stressing. This type of post-tensioning is usually referred to as an un-bonded post-tensioning system. Once installed, and the new cables spliced to the lock-off cable, concrete is poured and allowed to cure. As shown in FIG. 1, presently, a segment of polyvinyl chloride (PVC), polyethylene, etc., is used to cover the splice coupler. Then, devices such as pocket formers are used as caps on each end of the PVC to hold the cable in place inside the PVC. One problem with using a pocket former is that because pocket formers were not designed to be used as end caps, they do not tightly fit the PVC and can shift, allowing concrete to potentially enter the cavity.

Thus, there is a long felt need for an apparatus that tightly fits the ends of a tubular member, such as a PVC segment, when repairing concrete structures, to prevent concrete from entering the cavity of the PVC segment.

BRIEF SUMMARY OF THE INVENTION

The present invention broadly comprises an end cap secured to a tubular member for use in repairing post-tensioned concrete, including a first segment, a second segment, and a third segment. The first segment has a first end and a first opening, where the first segment is substantially cylindrical in shape. The second segment is substantially frustoconical in shape. The third segment has a second end and a second opening and is substantially cylindrical in shape. The second segment is disposed between and integral with the first segment and the third segment. A cavity is formed by the first, second, and third segments, where the first end is arranged to be secured to a tubular member and at least one cable is disposed longitudinally within the cavity.

In an embodiment, the end cap has an outer surface and an inner surface and the tubular member has an outer surface, an inner surface, a first end, and a second end, and the first end of the first segment is secured to the first end of the tubular member such that the inner surface of the end cap contacts the outer surface of the tubular member. Preferably, a second end cap is secured to the second end of the tubular member.

In an embodiment, the first segment has a first diameter (D1) and the third segment has a second diameter (D2), and the first diameter is larger than the second diameter. Preferably, the first diameter (D1) is approximately 2.375 inches and the second diameter (D2) is approximately 0.67 inches. Additionally, the first end of the tubular member has a third diameter (D3) and the third diameter (D3) of the first end of the tubular member is slightly smaller than the first diameter (D1) of the first segment.

Preferably, the end cap is made of plastic, such as polypropylene. However, it should be appreciated that the end cap may be made of metal, plastic, rubber, wood, etc., or any suitable material known in the art.

The present invention also includes a method of installing an end cap during the repair of a post-tension concrete structure, where the end cap includes a first segment, a second segment, and a third segment, the first segment having a first end, and the second segment having a second end. The method includes the following steps: (1) cutting an opening in a slab of concrete, (2) installing a temporary anchor device to transfer the load of at least one cable to the temporary anchor device, (3) cutting a section of the at least one cable, (3) removing a section of the at least one cable, (4) replacing the section of the at least one cable with a second section of at least one cable, (5) installing an encapsulated anchorage, (6) affixing a splice coupling to secure an end of the remaining at least one cable to an end of the second section of at least one cable and where the remaining at least one cable and the second section of the at least one cable are disposed within the splice coupling, (7) installing a tubular member, having a first end and a second end, to cover the splice coupling, (8) securing the first end of at least one end cap to the first end of the tubular member, (9) pouring concrete to fill the opening, (10) stressing the at least one cable after the concrete has cured and reached a specified compressive strength, and (11) removing the temporary anchor device. Preferably, after securing the first end of the at least one end cap to the first end of the tubular member, the method further includes securing the first end of a second end cap to the second end of the tubular member.

These and other objects and advantages of the present invention will be readily appreciable from the following description of preferred embodiments of the invention and from the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which:

FIG. 1 is a top plan view depicting two pocket formers disposed at opposite ends of a tubular member and a plurality of cables disposed therein;

FIG. 2 is a top plan view of two end caps disposed at opposite ends of a tubular member and a plurality of cables disposed therein;

FIG. 3 is a top plan view of the first end cap of FIG. 2 secured to the tubular member, shown with the plurality of cables removed;

FIG. 4 is a perspective view of the end cap and the tubular member of FIG. 3;

FIG. 5 is an exploded view of the end cap and the tubular member of FIG. 3;

FIG. 6 is a perspective view of the end cap of FIG. 3;

FIG. 7 is a front elevational view of the end cap of FIG. 3;

FIG. 8 is a right side elevational view of the end cap of FIG. 3;

FIG. 9 is a left side elevational view of the end cap of FIG. 3; and,

FIG. 10 is a cross-sectional view of the end cap and the tubular member taken generally along the line 10-10 of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects.

Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and, as such, may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. It should be appreciated that the term “substantially” is synonymous with terms such as “nearly”, “very nearly”, “about”, “approximately”, “around”, “bordering on”, “close to”, “essentially”, “in the neighborhood of”, “in the vicinity of”, etc., and such terms may be used interchangeably as appearing in the specification and claims. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described.

Adverting now to the figures, FIG. 2 is a top plan view of two end caps 10, 10 b disposed at opposite ends of tubular member 90 and plurality of cables 92 disposed therein and disposed in concrete 91. FIG. 3 is a top plan view of first end cap 10 secured to tubular member 90, shown with plurality of cables removed 92 removed. Generally, end cap 10 includes first end 11, second end 12, first segment 13, second segment 14, and third segment 15. Similarly, end cap 10 includes first end 11, second end 12, first segment 13, second segment 14, and third segment 15

FIG. 4 is a perspective view of end cap 10 and tubular member 90 of FIG. 3.

FIG. 5 is an exploded view of end cap 10 and tubular member 90 of FIG. 3.

FIG. 6 is a perspective view of end cap 10 of FIG. 3.

FIG. 7 is a front elevational view of end cap 10 of FIG. 3.

FIG. 8 is a right side elevational view of end cap 10 of FIG. 3.

FIG. 9 is a left side elevational view of end cap 10 of FIG. 3.

FIG. 10 is a cross-sectional view of end cap 10 and tubular member 90 taken generally along the line 10-10 of FIG. 2.

As shown in FIGS. 2 through 10, first segment 13 includes first end 11 and first opening 23. Preferably, first segment 13 is substantially cylindrical in shape. Second segment 14 is substantially frustoconical in shape. Third segment 15 includes second end 12 and second opening 24. Preferably, third segment 15 is substantially cylindrical in shape. Second segment 14 is disposed between and integral with first segment 13 and third segment 15. In particular, first segment 13 transitions into second segment 14 at first transition 19, whereas second segment 14 transitions into third segment 15 at second transition 21. For example, first segment 13 extends longitudinally towards first transition 19 and at first transition 19 second segment 14 begins to taper as second segment 14 extends towards second transition 21. At second transition 21, third segment 15 continues to extend longitudinally towards second end 12. Cavity 22 is formed by first segment 13, second segment 14, and third segment 15, where first end 11 is arranged to be secured to tubular member 90 and at least one cable, but preferably plurality of cables 92, is disposed longitudinally within cavity 22. In particular, plurality of cables 92 enter through second opening 24 of end cap 10, run longitudinally through first opening 23 of end cap 10, are spliced and secured via coupler 96, run longitudinally through a first opening of end cap 10 b and exit through a second opening of end cap 10 b, or vice versa, as the order can be transposed starting with plurality of cables entering through the second opening of end cap 10 b.

Second end cap 10 b has substantially the same configuration as first end cap 10. For example, first segment 13 b includes first end 11 b. Preferably, first segment 13 b is substantially cylindrical in shape. Second segment 14 b is substantially frustoconical in shape. Third segment 15 b includes second end 12 b. Preferably, third segment 15 b is substantially cylindrical in shape. Second segment 14 b is disposed between and integral with first segment 13 b and third segment 15 b. In particular, first segment 13 b transitions into second segment 14 b at first transition 19 b, whereas second segment 14 b transitions into third segment 15 b at second transition 21 b. For example, first segment 13 b extends longitudinally towards first transition 19 b and at first transition 19 b second segment 14 b begins to taper as second segment 14 b extends towards second transition 21 b. At second transition 21 b, third segment 15 b continues to extend longitudinally towards second end 12 b. Cavity 22 b is formed by first segment 13 b, second segment 14 b, and third segment 15 b, where first end 11 b is arranged to be secured to tubular member 90 and at least one cable, but preferably plurality of cables 92, is disposed longitudinally within cavity 22 b.

In an embodiment, end cap 10 further includes outer surface 16 and inner surface 18. Similarly, tubular member 90 has outer surface 93 and inner surface 94. Tubular member 90 further includes first end 95 a and second end 95 b. Additionally, first end 11 of first segment 13 is secured to first end 95 a of tubular member 90 such that inner surface 18 of end cap 10 contacts outer surface 93 of the tubular member 90. Preferably, second end cap 10 b is secured to second end 95 b of tubular member 90.

In an embodiment, first segment 13 has diameter D1 and third segment 15 has diameter D2. First diameter D1 is larger than second diameter D2. Preferably, first diameter D1 is approximately 2.375 inches and second diameter D2 is approximately 0.67 inches. Additionally, first end 95 a of tubular member 90 has third diameter D3 (not shown in the figures) and third diameter D3 is slightly smaller than first diameter D1 of first segment 13. It should be appreciated that third diameter D3 of tubular member 90 is slightly smaller than first diameter D1 in order to secure end cap 10 to tubular member 90 via an interference or friction fit. It should also be appreciated that the above dimensions are preferred; however, any of the elements of the end cap can be various sizes, shapes, and configurations suitable in the art.

Preferably, end caps 10, 10 b are made of plastic, such as polypropylene. However, it should be appreciated that the end cap may be made of metal, plastic, rubber, wood, etc., or any suitable material known in the art.

Moreover, the present invention is a method of installing end cap 10 during the repair of a post-tension concrete structure, where end cap 10 includes first segment 13, second segment 14, and third segment 15. First segment 13 has first end 11 and third segment 15 has second end 12. The method includes the following steps: (1) cutting an opening in slab of concrete 91, (2) installing a temporary anchor device to transfer the load of at least one cable, but preferably plurality of cables 92 to the temporary anchor device, (3) cutting a section of plurality of cables 92, (3) removing a section of plurality of cables 92, (4) replacing the section of plurality of cables 92 with a second section of plurality of cables 92, (5) installing an encapsulated anchorage, (6) affixing a splice coupling, i.e., coupler 96, to secure an end of the remaining plurality of cables 92 to an end of the second section of plurality of cables 92 and where the remaining plurality of cables 92 and the second section of plurality of cables 92 are disposed within coupler 96, (7) installing tubular member 90, having first end 95 a and second end 95 b, to cover coupler 96, (8) securing first end 11 of end cap 10 to first end 95 a of tubular member 90, (9) pouring concrete to fill the opening, (10) stressing the plurality of cables 92 after the concrete has cured and reached a specified compressive strength, and (11) removing the temporary anchor device. Preferably, after securing first end 11 of first end cap 10 to first end 95 a of tubular member 90, the method further includes securing first end 11 b of second end cap 10 b to second end 95 b of tubular member 90.

Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention. 

1. An end cap secured to a tubular member for use in repairing post-tensioned concrete, comprising: a first segment, having a first end and a first opening; a second segment; a third segment, having a second end and a second opening, the second segment is disposed between the first segment and the third segment; a cavity formed therein by the first, second, and third segments, wherein the first end is arranged to be secured to a tubular member and at least one cable is disposed longitudinally within the cavity.
 2. The end cap of claim 1, wherein the first segment is substantially cylindrical in shape, the second segment is substantially frustoconical in shape, and the third segment is substantially cylindrical in shape.
 3. The end cap of claim 2, wherein the second segment is integral with the first segment and the third segment.
 4. The end cap of claim 1, wherein the first segment has a first diameter (D1) and the third segment has a second diameter (D2), and the first diameter is larger than the second diameter.
 5. The end cap of claim 4, wherein the first diameter (D1) is approximately 2.375 inches and the second diameter (D2) is approximately 0.67 inches.
 6. The end cap of claim 4, wherein the end cap has an outer surface and an inner surface and the tubular member has an outer surface, an inner surface, a first end, and a second end, and the first end of the first segment is secured to the first end of the tubular member such that the inner surface of the end cap contacts the outer surface of the tubular member.
 7. The end cap of claim 6, wherein the first end of the tubular member has a third diameter (D3) and the third diameter (D3) of the first end of the tubular member is slightly smaller than the first diameter (D1) of the first segment.
 8. The end cap of claim 1, wherein a second end cap is secured to the second end of the tubular member.
 9. The end cap of claim 1, wherein the end cap is made of plastic.
 10. The end cap of claim 9, wherein the end cap is made of polypropylene.
 11. An end cap secured to a tubular member for use in repairing post-tensioned concrete, comprising: a first segment, having a first end and a first opening, wherein the first segment is substantially cylindrical in shape; a second segment, wherein the second segment is substantially frustoconical in shape; a third segment, having a second end and a second opening; wherein the third segment is substantially cylindrical in shape, the second segment is disposed between and integral with the first segment and the third segment; a cavity formed therein by the first, second, and third segments, wherein the first end is arranged to be secured to a tubular member and at least one cable is disposed longitudinally within the cavity.
 12. The end cap of claim 11, wherein the first segment has a first diameter (D1) and the third segment has a second diameter (D2), and the first diameter is larger than the second diameter.
 13. The end cap of claim 12, wherein the end cap has an outer surface and an inner surface and the tubular member has an outer surface, an inner surface, a first end, and a second end, and the first end of the first segment is secured to the first end of the tubular member such that the inner surface of the end cap contacts the outer surface of the tubular member.
 14. The end cap of claim 13, wherein the first end of the tubular member has a third diameter (D3) and the third diameter (D3) of the first end of the tubular member is slightly smaller than the first diameter (D1) of the first segment.
 15. The end cap of claim 11, wherein a second end cap is secured to the second end of the tubular member.
 16. A method of installing an end cap during the repair of a post-tension concrete structure, where the end cap includes a first segment, a second segment, and a third segment, the first segment having a first end, and the third segment having a second end, the method comprising the following steps: cutting an opening in a slab of concrete; installing a temporary anchor device to transfer the load of at least one cable to the temporary anchor device; cutting a section of the at least one cable; removing a section of the at least one cable; replacing the section of the at least one cable with a second section of at least one cable; installing an encapsulated anchorage; affixing a splice coupling to secure an end of the remaining at least one cable to an end of the second section of at least one cable and wherein the remaining at least one cable and the second section of the at least one cable are disposed within the splice coupling; installing a tubular member, having a first end and a second end, to cover the splice coupling; securing the first end of at least one end cap to the first end of the tubular member; pouring concrete to fill the opening; stressing the at least one cable after the concrete has cured and reached a specified compressive strength; and, removing the temporary anchor device.
 17. A method of installing an end cap during the repair of a post-tension concrete structure, where the end cap includes a first segment, a second segment, and a third segment, the first segment having a first end, and the third segment having a second end, the method comprising the following steps: affixing a splice coupling to secure an end of at least one cable to an end of the second section of at least one cable and wherein the remaining at least one cable and the second section of the at least one cable are disposed within the splice coupling; installing a tubular member, having a first end and a second end, to cover the splice coupling; and, securing the first end of at least one end cap to the first end of the tubular member.
 18. The method of claim 17, the method further comprising the following steps: before affixing the splice coupling to secure the end of the remaining at least one cable, cutting an opening in a slab of concrete; installing a temporary anchor device to transfer the load of at least one cable to the temporary anchor device; cutting a section of the at least one cable; removing a section of the at least one cable; replacing the section of the at least one cable with a second section of at least one cable; and, installing an encapsulated anchorage.
 19. The method of claim 17, the method further comprising the following steps: after securing the first end of at least one end cap to the first end of the tubular member, pouring concrete to fill the opening; stressing the at least one cable after the concrete has cured and reached a specified compressive strength; and, removing the temporary anchor device.
 20. The method of claim 17, the method further comprising the following steps: after securing the first end of the at least one end cap to the first end of the tubular member, securing the first end of a second end cap to the second end of the tubular member. 